Although many axon guidance molecules have been identified, the signaling and cell biological mechanisms leading to directed axon growth are still poorly understood. Building on our progress, we will ask in-depth questions about novel signaling and cell biological mechanisms of axon guidance. Specifically, we will use Frizzled3 phosphorylation and trafficking as a tool to solve how signaling asymmetry is generated in the growth cone and the cell biological mechanisms involved in turning. We will also use genetic mosaic approaches to study axon-axon interactions to address the unanswered question of how a group of axons pathfind together.